Circuit breakers for industrial use are classified by, among other characteristics, their interrupt rating and their fault current capability. Operation of the breaker involves the separation of arcing contacts of each phase by an actuating mechanism which is triggered by a tripping device. The actuating mechanism generally involves the triggered release of a spring-loaded rotating main shaft with short arms attached to pushrods which pull the contacts open when the main shaft opens. The actuating mechanism is designed to minimize the momentum of the moving parts for the mechanical stresses involved, so that the operating time for a tripping function is as short as possible. This is important, since typically, just a single uninterrupted current cycle is capable of passing enough energy to a failing device in the protected circuit to result in costly damage. In circuits where a very large fault current can be passed through the circuit breaker, the time needed for the breaker to exercise its normal tripping function may be long enough to permit the fault current to do serious damage to the equipment which is intended to be protected by the circuit breaker. This is due to the momentum of the relatively massive mechanical parts which must be moved in the course of a tripping operation. Therefore, it is common practice to locate a power fuse on the power supply side of the circuit breaker to deal with such situations in a controlled manner. The disadvantage of such an arrangement is that power fuses take up additional cabinet space, are relatively expensive, and require manual replacement for each fuse operation. Therefore, there is a need for a circuit breaker which is capable of reacting in a very short time to high fault currents.